Fair Value Measurements - Summary of Carrying Value and Estimated Fair Value of all Debt (Parenthetical) (Details)	Mar. 31, 2018	Aug. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Apr. 30, 2014	Feb. 28, 2013
3.50% Convertible Notes
Fair value measurement
Interest rate (as a percent)	3.50%		3.50%	3.50%		3.50%
3.50% Series A Convertible Notes
Fair value measurement
Interest rate (as a percent)	3.50%		3.50%		3.50%
3.75% Convertible Notes
Fair value measurement
Interest rate (as a percent)	3.75%	3.75%	3.75%